Laser Cutter fault light - water pump noisy bearings

[Gavin Jackson]

Guys

The laser cutter appears to have an issue with the water pump.

After a few hours of work tonight, the fault light appeared.

I checked the water flow rate gauge and it was half the rate I observed earlier.

Having a listen to the pump, it sounds like it is a bit tired.

I am happy to donate an attwood V625 bilge pump if is of any use.

I have tagged the unit as out of service until it can be investigated further.

Regards,

Gavin

[Gavin Jackson]

Guys, 

Somewhat of an update.

I have fitted the bilge pump tonight and the flow rate s 1.7-1.8 LPM.

Temperature is sitting at 12.1 degrees.

The fault light is on and fails to extinguish unless the flow rate momentarily exceeds approx. 2 LPM.

I guess the cold water and consistant flow rate from the pump is no longer an issue (At the present).

I will power it off until someone will figure out how to extinguish the fault light.

As an aside, Is there any reason that the little water flow display cannot be mounted on the top of the cutter where it is easy to view.

- Gav

[Darren Freeman]

On Thu, 2014-04-17 at 02:00 -0700, Gavin Jackson wrote:
> I have fitted the bilge pump tonight and the flow rate s 1.7-1.8 LPM.

This is below the minimum that I've set in firmware. The original pump
happily did 3.5 LPM, and I'd rather not see an inferior pump
substituted. I set it to flash the fault light at 2.5 LPM and cut out
entirely at 2.0 LPM.

We don't have any specifications for this tube, but in general the
performance of the tube will suffer if it is allowed to overheat.

I got a chance to inspect the dead tubes that came with the cutter, and
they may have suffered from loss of cooling when they failed. Both had
suffered from mechanical failure of the glass envelope.

> The fault light is on and fails to extinguish unless the flow rate
> momentarily exceeds approx. 2 LPM.

As above. The fault light is itself not faulty.

> I guess the cold water and consistant flow rate from the pump is no
> longer an issue (At the present).

Actually, it is an issue if it's below the set-point!

We can decide to revise the minimum, of course, but it was set to a
value which would indicate a serious problem with the other pump. I
revised it down several times before drawing a line in the sand, so to
speak.

The flow rate continued to decrease, forcing Rob and Lauren to clean out
the biological contamination on at least one occasion each. It may be
that your original problem was not the pump, but further contamination.

The reason that the chiller runs on a separate, isolated loop, is that
it's mine and I don't want it full of slime that I then have to
disinfect and clean out. The fact that it keeps returning is not
encouraging!

Also, it would be better if the space were not depending on that
chiller. I have a different one to donate, but I can't get the damn
thing to Melbourne at the moment. An office water cooler should be
plenty for this application, if somebody comes across one going free to
a good home.

> I will power it off until someone will figure out how to extinguish
> the fault light.

Increasing the flow rate would work :)

That would be, IMHO, the most preferable solution. I would like to see a
proper non-garden-fountain pump be used with this machine.

> As an aside, Is there any reason that the little water flow display
> cannot be mounted on the top of the cutter where it is easy to view.

Because I'll be taking it home again when I've wired up the 20x4 display
that's already on the front panel, above the fault light. It's just
living there temporarily, as it shouldn't concern most users. Unless the
machine is dead, in which case it's no hassle to view it where it is.

My work on the laser cutter was interrupted by various life events.
Although I didn't make it as nice as I had planned, this time around, I
am at least glad that the only working laser tube is still working :)

I leave it to others to figure out how to get the DOA tube replaced by
the manufacturer. The day is coming when we will wish we had it
available; cheap sealed CO2 tubes simply don't last that long.

Have fun,
Darren

[Lauren Shearer]

I doubt that a pump designed to cope with dirty water and pumping at slightly higher flow rates (1.8-2.1 Lpm) is "inferior" to one that we know is fouled in the impeller, is not designed for fouled water, and is pumping 1.1-1.7 Lpm at the moment - not long after the most recent clean.

The issue I have with the flow meter is that it's a secondary indicator causing a top-level failure. That is, regardless of the actual tube safety it's being turned off by a black box.

If the tube is at 12 degrees (ambient 21) then flow is secondary. Not irrelevant, but it is a diagnostic indicator, not the actual safety related one. Temperature is the main one.

To use the absurdity test, a flow rate of 1000 Lpm would not be fine if the water were 99.9 degrees

I'd prefer you didn't have to put too much more time/effort into the machine given your recent heroic contribution (I know there was more than one all-nighter). May I suggest checking with one or more committee members before undertaking significant public works? I'd also be more comfortable if the firmware / wiring was public.

I believe the custom pcb is based in the Mega, with firmware based on marlin, so would it not have a number of analog lines that could be used for sensors and enough processor time to run the LCD?

[Joshua Mesilane]

If it helps, I gave a couple of 1" inlet 1" outlet 240v water pumps at home I'd be happy to donate. You could regulate the flow down with a simple valve arrangement.

These are "retired" house pumps where the cheap, nasty pressure switch had failed. The pumps themselves are fine

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[Luke Weston]

Maybe just buy something new that is known to be reliable, with known engineering data and serviceability.
I know there is a bit of a fascination around here sometimes with using recycled donated junk, or buying cheap mystery stuff from AliBaba, and an adversity to spending the organisation's money on any quality infrastructure in the hopes that somebody would come along and donate something cheaper, but I would do it properly with a new pump, personally, for reliable, lasting infrastructure.

The German-made Eheim stuff is very good, has spare parts and engineering data available, is designed to be serviced, and designed to run 24/7 in professional aquarium installations.

https://www.eheim.com/en_GB/products/technology/pumps/compact_plus#downloads

http://www.aquaticsupplies.com.au/aquatic-supplies-australia-eheim-compact-wet-and-dry-2000-pump-2000l-h.html

https://www.eheim.com/resources/product//28/downloads/11/EHEIM_compact+_2000_3000_5000_manual.pdf
The pump curve (flow rate vs. head) for the series is here: http://www.masa.asn.au/phpBB3/viewtopic.php?p=703703

If you look at a typical Wun Hung Lo cheap laser chiller (http://www.cncoletech.com/Laser%20Water%20Chiller.html), they quote a flow rate of 15 L/min. That is the maximum flow rate, right at the maximum flow rate end of the pump curve. This is not the flow rate that you will empirically observe in the real world, when the pump is pumping against some head - it will be somewhere in the middle of the pump curve.

The 2000l/h for the Eheim Compact Plus 2000 is over twice that, which I think is fine.

Also, what are you powering the pump from? It looks suspiciously like that 12V bilge pump is connected to a dodgy looking switchmode module intended for powering downlights or something - a constant current driver for LED downlights? Is it fit for purpose, to meet that pump's specifications of voltage and current? If it's not, that wouldn't surprise me as a likely cause of the pump not producing results that you expect.

The pumps I recommend are 240V pumps, but anyway, if there's some insistence from the rest of the community on using a low-voltage DC pump I will bring an appropriate DC rail out to the side of the machine on the side where the 240V GPOs are and wire it in nicely to an outlet socket on the chassis, supplying a voltage and current to meet the specifications for the pump that is supplied. I don't want this to be some ugly dodge looking cupcake-style messy science fair project where other people have come along and grafted on three separate external mains power supplies, all of which need to be plugged in and working, because this just creates more potential for failure and user complexity.

I'll also replace the dodgy 50-year-old telephone wire (?), non-sticky adhesive and external plugpack that powers the internal LED strips that somebody added in, at the same time. Ultimately I'm not going to stand there guarding the laser cutter 24/7, so when other people come along and graft stuff into it ultimately you're responsible for it - I'm not supporting it, you need to seek out the person who did that work in order to get instructions or support. And if it's good work they get the credit, and if it's not so good work, they also get the credit/responsibility. By all means give credit where credit is due, but if it's not work that I did then don't come to me with blame/support/responsibility - direct that to the persons where it is due, and I'm sure the appropriate persons will provide support and responsibility for the work.

Also, I'm not exactly sure what the best choice of biocide is, if any, but I don't think potassium permanganate is a good choice. Because it is such a strong oxidiser it will rapidly and completely be reduced by just about any crap that is hanging around in the environment, leaving a brown mud of manganese dioxide. The biocide, if any, needs to be insoluble and remain insoluble, and needs to not be corrosive to copper or any other metals that may be encountered in the plumbing.

Also, I think the water vessels need to be completely sealed from the outside environment, not open, to prevent dust/dirt/foreign crap ingress.

Coherent has a document here on cooling water guidelines for their Ar/Kr ion heads (not CO2 lasers, but this is irrelevant):

www.coherent.com/Downloads/ACF97.pdf

They say that biocidal additives should be completely avoided in their gear, and that shortwave UV irradiation be used to prevent biofilm/algae/whatever growth if this is a problem. I don't know if there is any rationale behind that other than just chemical reactivity/corrosion concerns.

Flushing all existing crap out of the primary cooling circuit, filling it with clean distilled water, and having it completely enclosed against dust ingress is probably a good place to start.

EDIT: Josh, you mean an actual mains pressure, big ass pump for pumping the main water feed from your tank up to your house? Hmm, that seems like a tiny bit of overkill.

Regards,
  Luke

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[Luke Weston]

Edit because I have not had one milligram of caffeine today:

"The biocide, if any, needs to be insoluble and remain insoluble"

That should say, of course, soluble and remain soluble.

[Darren Freeman]

On Fri, 2014-04-18 at 17:16 +1000, Luke Weston wrote:
> I know there is a bit of a fascination around here sometimes with
> using recycled donated junk, or buying cheap mystery stuff from
> AliBaba, and an adversity to spending the organisation's money on any
> quality infrastructure in the hopes that somebody would come along and
> donate something cheaper, but I would do it properly with a new pump,
> personally, for reliable, lasting infrastructure.

I agree. I think most of us suffer from under-valuing our own time. If
you can get it working for next to nothing in just a few hours, then
you've saved a few dollars at the expense of a few hours. That might
seem worthwhile to a student or an unemployed person, but it's not
really fair of an organisation to value its volunteers' time at zero. It
also doesn't make economic sense, since you have a limited amount of
volunteer time to make use of.

I believe the people who are most likely to pay the full membership fee
every month are often people with little time to waste on things not
working. It hurts the bottom line if we can't keep equipment working,
and so people lose interest. (Even one person, really, for how much is a
pump worth?)

I'm not saying we should splash money around. Sometimes you can easily
afford to gamble on something working, and often the educational
experience is worth a lot as well. But I remember the last time the
laser cutter went down for an extended period, and I didn't feel good
about it. It's a unique piece of equipment, and I can't think of where
I'd go if I couldn't use it.

For what it's worth, Dave has in the past said to just buy the right
items for the laser cutter. I think maybe he hasn't been approached with
a specific request.

And it is fair to see whether someone has something perfectly
serviceable, first. But as has been pointed out, the equipment is now
down because of this. The conversation has gone in the direction of
whether or not the flow rate really needs to be what it was, instead of
just keeping it how it was.

> I don't want this to be some ugly dodge looking cupcake-style messy
> science fair project where other people have come along and grafted on
> three separate external mains power supplies, all of which need to be
> plugged in and working, because this just creates more potential for
> failure and user complexity.

On the one hand, yes this creates complexity and redundancy, but on the
other, it's less likely that a short or EM interference will have a
direct effect on the internal circuitry. It's basically a modular
approach, with pros and cons.

It seems to me that the biggest problem is in documenting what the
system looks like now, as well as changes to it over time, and who made
those changes. Modularity makes it easier to add things and change
things, but if you don't occasionally turn prototypes into final
implementations, then you will end up with a mess.

If it were me, I wouldn't like to mess with the internals if they aren't
documented! So I probably would have used plug-pack power supplies too,
at least initially.

There's also the issue that there isn't an internal 12 V rail (that I
know of). We have 24 V and (I think) 36 V. So it's also a planning
issue. It's so much easier to stick a plug-pack on the side and not risk
interfering with what someone else might be doing.

> By all means give credit where credit is due, but if it's not work
> that I did then don't come to me with blame/support/responsibility -
> direct that to the persons where it is due, and I'm sure the
> appropriate persons will provide support and responsibility for the
> work.

I hope this hasn't been happening to you, Luke.

For the record, last time I had an issue in which I needed to know about
something you had done, I simply phoned you up and you emailed me a PDF
of the schematic. I had it diagnosed and fixed soon after.

Extensive documentation is nice, but we're all volunteers here. Let's
not pretend we don't have each other's mobile numbers, or that there are
problems which simply must be solved right now with guesswork, because
we don't have certain information at hand.

Creative types often find it really draining to have to stop what they
are creating, in order to update documentation. This is an additional
cost if we can't communicate verbally.

> Also, I'm not exactly sure what the best choice of biocide is, if any,
> but I don't think potassium permanganate is a good choice. Because it
> is such a strong oxidiser it will rapidly and completely be reduced by
> just about any crap that is hanging around in the environment, leaving
> a brown mud of manganese dioxide. The biocide, if any, needs to be
> insoluble and remain insoluble, and needs to not be corrosive to
> copper or any other metals that may be encountered in the plumbing.

I chose KMnO4 because:

* it is cheap and available around the corner
* it has been used as a biocide in industry
* it is effective at low concentrations
* it is (I believe) compatible with the materials in use
* it is not some proprietary unknown mixture intended for another
purpose
* it looks nice when it's still purple

I didn't have much else to base a decision on. Desperate times and all
that. The slime was winning!

I think the brown colour is slime that has been stained. If the system
were sparkling clean, it shouldn't be discoloured.

But, you know, I haven't seen it in a while. If the slime keeps winning,
then it's not very effective.

> Also, I think the water vessels need to be completely sealed from the
> outside environment, not open, to prevent dust/dirt/foreign crap
> ingress.

This isn't the main problem, however.

> Coherent has a document here on cooling water guidelines for their
> Ar/Kr ion heads (not CO2 lasers, but this is irrelevant):

Actually it is somewhat relevant. AFAIK, all of these tubes use metal
and alumina ceramic, not glass. I have heard of mildly acidic coolants
eating through ion laser tubes of the glass/ceramic type.

A CO2 tube is a lot more like a piece of laboratory glassware.

> They say that biocidal additives should be completely avoided in their
> gear, and that shortwave UV irradiation be used to prevent
> biofilm/algae/whatever growth if this is a problem. I don't know if
> there is any rationale behind that other than just chemical
> reactivity/corrosion concerns.

I've run them with whatever process coolant was supplied by my
university (propylene glycol and corrosion inhibitors). I can tell you
that the water was pink, would you like to know more? :)

Commercial coolants contain biocides.

I did contemplate using car radiator coolant, but that is toxic, and I
can foresee that we spill it everywhere.

Maybe it is time to track down and invest in some propylene glycol based
coolant, and see if it fouls up.

> Flushing all existing crap out of the primary cooling circuit, filling
> it with clean distilled water, and having it completely enclosed
> against dust ingress is probably a good place to start.

I haven't personally noticed dust being a problem. But yet another flush
with bleach, and then making it more light-tight, would probably help.
It's basically a heated aquarium at the moment, and it sits under a
window.

Maybe add a few snails, or sucker catfish? :)

Have fun,
Darren

[Nathan Rose]

I was hoping to use the laser cutter on Tuesday. Can I get a clarification from someone who understands this thread better than me whether these faults are the 'Definitely Do Not Use' sort or more of a 'This Is An Issue We Need To Fix Long Term, But It Should Be Fine For Now' kind of thing?

[Lauren Shearer]

This is by no other sanction than my own:

If the pump is running, and the temperature gauge within the electronics box indicates the tube is at less than 50 degrees, you can use it (pending all other accreditation / learning )

The watchdog circuit will beep at you the first time you arm the laser and intermittently thereafter, from observation this occurs even after the flow picks up to 2.2 - 2.4 Lpm. The fault light itself will flash once every four-five seconds (have not sat with stopwatch). The high voltage circuit does not appear to be cut by the watchdog circuit.

As the watchdog system is not disconnecting the high voltage and is not integrated into the core controller, it does not prevent you from using the system. Of course, it then behooves you to be aware of the flow rate and temperature at all times (just pump noise is not enough)

[Darren Freeman]

On Sun, 2014-04-20 at 03:09 -0700, Lauren Shearer wrote:
> If the pump is running, and the temperature gauge within the
> electronics box indicates the tube is at less than 50 degrees, you can
> use it (pending all other accreditation / learning )

That would not be healthy in the long term, but fingers crossed it may
not cause a sudden and costly failure.

I say "may" because I haven't tried it. If it belonged to me personally,
and if I were fairly desperate, I would probably run it like this. But
it doesn't, and a number of people would be upset if it failed.

As it stands, it won't work, so there's no point unless you also perform
modifications to override the over temperature interlock, which would
cut the laser at 35 deg. C.

If you are reaching this temperature, then something unexpected is
happening. It is prudent to diagnose and correct any such fault instead
of attempting to run it anyway.

> The watchdog circuit will beep at you the first time you arm the laser
> and intermittently thereafter, from observation this occurs even after
> the flow picks up to 2.2 - 2.4 Lpm. The fault light itself will flash
> once every four-five seconds (have not sat with stopwatch). The high
> voltage circuit does not appear to be cut by the watchdog circuit.

Unless someone has deliberately changed the configuration, the HV will
be cut at <2.0 LPM flow rate and/or >35 deg. C inlet temperature.

Such a modification would not be hard to do, but let's be clear that I
left it in a state where it would be pretty difficult to kill the laser
due to loss of cooling. Now I hear that some experimentation is going
on, and if that safety system has been defeated, then I am not
responsible for the outcome.

Have fun,
Darren